The present invention relates to the oxidation of hydrocarbon compounds and halogenated organic compounds. In particular, the invention relates to methods for the removal and destruction of organic compounds from liquid and gaseous streams by the essentially complete oxidation of halogenated organic and hydrocarbon compounds to carbon dioxide, haloacid and water in the presence of a carbonaceous catalyst.
Halogenated organic compounds are useful for a number of purposes. In most applications of these materials, particularly in their use as solvents, the spent materials are discarded. The production and use of these halogenated organic compounds often result in the generation of unwanted halogenated organic compound byproducts, which represent a waste of both the halogen and organic compounds thereof. The capital investment required for the further processing of spent and unwanted halogenated organic compounds to provide useful materials often exceeds the value of such processing and these unwanted halogenated organic compound byproducts must be discarded.
Hydrocarbon compounds are useful for a number of purposes, in particular, as fuels, solvents, degreasers, cleaning agents, and polymer precursors. The most important source of hydrocarbon compounds is petroleum crude oil, refined into separate hydrocarbon compound fractions by well-known processing techniques. Many uses of hydrocarbon compounds yield contaminated gaseous and liquid streams which must be discarded or processed for reuse. Thus, there are many opportunities for hydrocarbon compounds to escape into the environment.
Processing and storage of these halogenated organic and hydrocarbon compounds often lead to contamination of the environment (such as soil, groundwater or the air) through accidental spills, leaks from processing equipment and evaporative losses, even though the processor or user of the compounds exercises the utmost care in handling the compounds. Because of their solubility in water and, in many cases, their chemical stability, disposal of these organic compounds by releasing them into the atmosphere or flushing them away with water can cause serious pollution, leading to problems arising from the possible carcinogenic and general toxicity of some of the organic compounds.
Typical disposal methods for undesirable halogenated organic and hydrocarbon compounds and their by-products consist primarily of terrestrial burial methods. Additional disposal methods include ocean discharge, open pit burning, venting to the atmosphere and deep-well disposal. However, these methods are known to contaminate soil, ground water and air and are considered hazardous to the environment. In addition, these methods are economically unattractive because the cost of the disposal of the unwanted organic compounds and their byproducts is not diminished by recovery of some materials of significant economic value.
It is desirable, therefore, to remove these halogenated organic and hydrocarbon compounds from the environment, especially from air supplied for breathing to portable air packs, process plant control rooms, "clean rooms" in silicon chip manufacturing plants and other controlled-environment rooms. Methods for eliminating halogenated organic and hydrocarbon compounds from the environment, such as catalytic incinerators, are known in the art.
Incineration of undesirable halogenated organic compounds also has been proposed. U.S. Pat. No. 3,453,073 discloses a process for recovering halogen from halogenated hydrocarbons comprising passing a chlorinated hydrocarbon, water and oxygen over catalysts at elevated temperatures to form oxides of carbon, water, and hydrogen chloride. This process, however, requires elevated temperatures using special equipment that is stable at such high temperatures and resistant to corrosion by the hydrogen chloride and water produced. The production of carcinogenic materials such as dioxin also is a serious impediment to this disposal method.
U.S. Pat. Nos. 3,989,806 and 3,989,807 propose a process for the recovery of chlorine from chlorinated organic compounds which comprises catalytically oxidizing a chlorinated organic compound feed by reaction with oxygen or an oxygen-containing gas at a reaction temperature of below 500.degree. C. and in the presence of a transition metal-containing supported catalyst. The catalytic supports employed in this method include zeolite materials and activated alumina.
Catalytic incineration of undesirable hydrocarbon compounds using a variety of catalysts is also known. The hydrocarbon compounds to be destroyed are removed from a liquid by countercurrent stripping with air, nitrogen, or other gas stream which will carry hydrocarbons. Hydrocarbons are often removed from soil by passing a gas, such as air, through the contaminated soil. The gas containing hydrocarbon vapor then is passed over the catalyst, typically at elevated temperature (significantly above 250.degree. to 300.degree. C.), with residence times sufficient to oxidize the hydrocarbon. In addition to the additional energy cost incurred in heating catalyst, reactants, and inert material carried with the reactants (such as nitrogen with the oxygen in air), such high-temperature methods require that the material of construction of the processing apparatus be capable of resisting the temperature utilized. Further, at higher temperatures, there exists the possibility of producing noxious or deleterious compositions, such as NO.sub.x if nitrogen is present during the oxidation, which are not normally produced at lower temperatures.
A catalyst for complete oxidation of gaseous hydrocarbon mixtures is disclosed in DD 280,395. The catalyst comprises an oxidation component, preferably CuO, and an adsorption component, preferably an aluminosilicate. Processing temperature preferably is 407.degree. to 577.degree. C.
A system for solvent recovery and disposal of contaminants released by regeneration of solvent-laden air adsorbers is disclosed in U.S. Pat. No. 5,149,342. This system involves condensation/cooling of regenerant streams, recovery of the the solvent/contaminants by decantation, phase separation, liquid extraction and distillation steps with incineration of unreclaimed contaminants from activated carbon adsorbers.
A system for the removal and disposal of airborne contaminants from paint booths by adsorbing contaminants on activated carbon, regenerating the adsorbent, recovering the regenerant fluid by various separation, purification and distillation steps, and incinerating the contaminants at 700.degree. to 2500.degree. F. is disclosed in U.S. Pat. No. 4,689,054.
A catalytic process which converts volatile organic compounds (VOC) in aqueous waste streams into carbon dioxide and water is disclosed in Chemical Engineering 99 (8), 19 (Aug. 1992). The catalyst disclosed is platinum or palladium on a carbon carrier which is coated with poly(tetrafluorethylene); the catalyst passes vapors but not liquids.
Adsorbents for hydrocarbon and halogenated organic compounds also are available. Methods for regenerating saturated adsorbents and catalysts used to remove harmful organic compounds from water, soil, or air are known. Typical regeneration methods include steam regeneration, superloading the catalyst and solvent regeneration. The drawback of these methods is that although the adsorbent or catalyst may be regenerated, the steam or solvent effluent stream remains contaminated with the harmful organic compound and must be treated before disposal.
A need exists, therefore, for an environmentally safe method of disposing of halogenated organic and hydrocarbon compounds which does not require extra separation steps that subject the environment to further contamination (such as decanting, liquid/liquid extraction, distillation and the like), which does not expend large amounts of energy (such as the condensing and reheating/revaporizing steps involved in incineration), and which does not require high operating temperatures and special temperature/corrosion resistant materials of construction (such as conventional incinerators operating at about 500.degree.-1000.degree. C.).
The present invention overcomes many of the disadvantages of previous organic compound disposal methods. It is an object of the present invention to provide a process for the removal and destruction of harmful halogenated organic and hydrocarbon compounds in fluid streams which have been contaminated by contact with other contaminated materials (such as soil, water or air), with a minimum number of separation/handling steps in the treatment process, with reduced energy requirements and with relatively low operating temperatures which do not require the use of specialized equipment.